150mg test a week should be more than enough to make steady progress from where you are at the moment.
This, I suspect, is your major issue.
W all have to accept that lifting, and gaining a bit of muscle, is a long, painful process. There's no real short cuts, and no comfortable way to achieve this. Decent test levels are nice but not essential to this. There are countless studies showing people with low test can build muscle.
I've been on prescribed trt for 8 years now and my trough levels are often single figures but I still make progress. Prior to my trt my test levels were found to be 'undetectable' and, although I have no idea how long I had been that way, I still carried more muscle than most. Then again, I've been training for 38 years solid.
Strong mentality is the greatest tool in a lifters bag. The ability to train for 3 or 4 hours every week, thoughtfully and progressively, for year after year after year is the secret to gaining and maintaining muscle. And you have to do this whether you feel good or bad, up or down. It's brutal and it's relentless, but it's what you need to succeed regardless of levels of testosterone.
The only thing you need to do before returning to the gym is....Clear your head. Make a plan and get on with it. If you stick to it you will gradually become encouraged and results will follow.